pickle.py bytearray memoization bug with protocol 5

[cfbolz]

BPO	43907
Nosy	@pitrou, @cfbolz
PRs	bpo-43907: add missing memoize call in pure python pickling of bytearray #25501

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-04-23.21:28:19.068>
created_at = <Date 2021-04-21.18:08:15.207>
labels = ['type-bug', 'library', '3.10']
title = 'pickle.py bytearray memoization bug with protocol 5'
updated_at = <Date 2021-04-23.21:28:19.066>
user = 'https://github.com/cfbolz'

bugs.python.org fields:

activity = <Date 2021-04-23.21:28:19.066>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2021-04-23.21:28:19.068>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2021-04-21.18:08:15.207>
creator = 'Carl.Friedrich.Bolz'
dependencies = []
files = []
hgrepos = []
issue_num = 43907
keywords = ['patch']
message_count = 3.0
messages = ['391537', '391737', '391738']
nosy_count = 2.0
nosy_names = ['pitrou', 'Carl.Friedrich.Bolz']
pr_nums = ['25501']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43907'
versions = ['Python 3.10']

[cfbolz]

The new codepath for the BYTEARRAY8 bytecode is missing memoization:

>>> import pickletools, pickle
>>> b = (bytearray(b"abc"), ) * 2
>>> b1, b2 = pickle.loads(pickle.dumps(b, 5)) # C version
>>> b1 is b2
True
(bytearray(b'abc'), bytearray(b'abc'))
>>> b1, b2 = pickle.loads(pickle._dumps(b, 5)) # python version
>>> b1 is b2 # :-(
False

Found it because PyPy is using pickle.py with no C implementation. I'm preparing a patch.

[pitrou]

New changeset 1e9f093 by Carl Friedrich Bolz-Tereick in branch 'master':
bpo-43907: add missing memoize call in pure python pickling of bytearray (GH-25501)
1e9f093

[pitrou]

Thanks for the report and fix!